The use of plastics materials as a substitute for metals in the manufacture of housings, containers and components of machines and appliances is greatly expanding. Plastics materials are generally flammable and there is a danger of fire in such machines should ignition occur.
When plastics materials are exposed to heat or fire they can melt and/or ignite releasing toxic volatiles and exhibiting problems associated with oil based fires. Fire retardants can be added to plastics materials but the service life of those retardants is often substantially less than the service life of the plastics components. Typical fire retardants are relatively volatile and vaporise from the plastics material over time. Furthermore, if the fire is fierce, then the fire retardants can be driven from the plastics materials before the fire reaches them, rendering the fire retardants effect null.
If an appliance or machine containing plastics materials catches fire, it is important to detect the fire as early as possible in order to control and extinguish it. There are many means of detection of fire including smoke, heat, light and gas emissions. Within a machine or appliance, the choice of the means of detection of a fire will be made on the basis of early and reliable detection, and the cost of the detection means.
The most likely cause of a fire in an appliance or machine which is otherwise operating normally is by a failure in the electrical systems within the appliance or machine. Electrical failure is generally by overheating and then short circuit of electrical components which generates severe local heating and then ignition of the overheated components when the short circuit finally occurs. In many cases of such fires, the ignition by short circuit is likely to cause any fuses protecting the supply wiring to go open circuit since the short circuit generally results in a sudden increase in current. It must therefore be assumed that when fire occurs in appliances or machines that there is no power supply available to the fire detection system or the fire extinguishing system. The assumption that the appliance or machine has no power supply at the time of ignition makes early detection of the fire even more important since there is no ready source of energy available to operate the fire extinguishing system.
The factors considered above make it essential that any fire detecting and extinguishing system to be installed in an appliance or machine must have a self contained source of energy of sufficient magnitude to power the fire detection means for a period of time after the interruption of the power supply during which a fire might manifest itself. The power supply must then still have sufficient energy to activate a fire extinguishing system should a fire be detected during this time. Many such sources of energy are available such as rechargeable electric batteries and electronic capacitors. Each of these sources have limitations. Electric batteries require sophisticated charging circuits and the types presently available do not have working lives which would extend over the period of time represented by the life of most appliance or machines. Since most appliances and machines are sold into markets which there is an expectation that the appliance or machine will not require service then there is no ready means of assuring that the battery will be kept in good working order for the life of the appliance. Electronic capacitors are considerably more reliable than electric batteries and require less sophistication in keeping them charged during the operation of the appliance or machine. However, electronic capacitors can only store a small amount of energy and for a limited time compared to an electric battery.
When the preferred method of storing energy is an electronic capacitor due to its reliability and cost, then there is only a small quantity of energy available to operate a fire extinguishing device in the event of a fire. For reliable operation of the fire extinguishing device, it must be able to operate with very small quantities of electrical energy. Since the fire extinguishing device must be able to distribute substantial quantities of fire extinguishing material throughout the appliance or machine in order to be effective then it must have access to substantial quantities of energy. Such a fire extinguishing material is a water based Aqueous Film Forming Foam, a commercially available fire extinguishing material which is particularly effective at extinguishing fires in plastic based materials.
Therefore, if only very small quantities of energy available to initiate the fire extinguisher from electronic capacitors at the start of a fire and then substantial quantities of energy are required to distribute the fire extinguishing medium, then there is a requirement for a mechanism capable of amplifying or cascading the available energy sources up to the level required of the fire extinguishing material.
Even though the present invention will be primarily described in relation to fire extinguishment it will be appreciated that in its broadest form it is not limited to that specific application.